Sartyr, known in Japan as Kabayama 「樺山, Kabayama」 is the head teacher at the Ra Yellow dormitory at Duel Academy with the alias of Don Simón (which is the name of a Spanish brand of juices and other beverages) or Curry Mask 「カレー仮面, Karē Kamen」 in the Japanese version.
Sartyr has the sad honor of being the least featured of the three main professors. He is seen on occasion in the first season, notably in episode 2 at the Ra Yellow welcoming dinner shot. He is an accomplished chef as well as the card design teacher in the school.
His only Duel was against Tyranno Hassleberry in episode 63, to try and force him and his non-Slifer Red friends to return to their old dorms. He does this because he is almost completely ignored or overlooked by nearly everyone in the Academy and with everyone else in his dorm either graduated or promoted to Obelisk Blue.
However, he also does this because it was while Vice-Chancellor Bonaparte was trying to eliminate the Slifer Red dorm and his job would have been made easier with the students moving back to Ra Yellow.
He feels lonely and rejected; his lack of attention is so great, that not even Bonaparte who is watching his Duel with Hassleberry from the nearby forest recognizes him at first when he is unmasked.
Ultimately, he is defeated by Hassleberry, though Hassleberry promises to return to the Ra Yellow dorm "from time to time" if Sartyr continues to cook curry.
In Yu-Gi-Oh! GX Spirit Caller, Sartyr runs a Deck called "Delicious Recipe". You must defeat him to get a Ra Yellow uniform. His primary role in the game is in the Academy's Library, where you can duel again him in Duel Puzzles and look up tips for using certain cards.